<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
         console.log(parseInt(""));     //  NaN
         console.log(parseInt(3.14));   //  3
         console.log(parseInt("4.12"));  // 4
         console.log(parseInt("abc123"));// NaN
         console.log(parseInt("123abc"));// 123
    </script>
</body>
</html>